Summary Metered dose inhalers represent a large proportion of inhaled products used in the treatment and prevention of asthma and chronic obstructive lung disease. These products were developed in the middle of the last century and have changed little in the intervening period. One significant change was the replacement of ozone depleting chlorofluorocarbon (CFC) propellants with more environmentally friendly hydrofluoroalkanes as both the suspending medium and the means by which drug is generated as an aerosol. The role of co-solvent and surfactants in the performance and the quality of the product is significant. The pharmaceutical industry performed the Herculean task of reformulating all of their inhaled products into the new propellants quickly and efficiently to accommodate the impending international phase out and elimination of CFCs. Despite the success of their endeavors there remains a need for a systematic evaluation of excipient effects on the efficacy of metered dose inhaler products. It is proposed that controlling key manufacturing variables and measuring a range of quality and performance attributes will highlight factors contributing to accuracy and reproducibility of the delivered dose and aerodynamic particle size distribution. These outcomes are relevant to efficacy, and important for development of predictive models. The specific aims of the proposal are: Selection of drug and preparation in a range of primary sizes suitable for delivery as a respirable aerosol; evaluation of the effects of (a) different amounts of co-solvent (ethanol) and surfactant (oleic acid) will be evaluated. A multivariate statistical design will be employed to optimize the manufacture and maintain efficiency without losing study power. A range of concentrations of the additives will be employed to explore process design space within and outside the Q2 acceptance limits of 5% and (b) other surfactants will be studied based on the experience gained with oleic acid and principles of physical chemistry; construction and utilization of mathematical models to describe the influence of formulation and device variables on performance of the metered dose inhalers. The important variables in pMDI product manufacture that may impact on performance include: drug substance and its intrinsic physico-chemical properties; particle size and distribution of milled particles for suspension formulations; composition of the formulation with respect to: Propellant; Co-solvent; Surfactant; formulation, device (canister, valve and actuator) interactions. Important quality and performance variables include: delivered dose and uniformity; aerodynamic particle size distribution; plume geometry and spray pattern and; potentially dissolution (for poorly soluble or delayed dissolution materials) The intent by regulatory agencies to design quality into products based on sound scientific and engineering principles requires that the manufacturing variables and the testing protocols and procedures are suitable to achieve the desired monitoring and control of the product. It is the intent of this project to develop a framework from which to develop criteria for product performance based on control of input process and product variables.